1. Field of the Invention
The present invention relates to a method for the treatment of oil drill cuttings.
2. Discussion of the Background
As is known, the function of drill mud is to strengthen the walls of the oil well hole, protect metal parts from corrosion, cool and lubricate the bit during drilling. Mud, which can be aqueous-based or oil-based, also provides pressure for keeping the geological formation intact and helps to carry the cuttings produced by the action of the bit in digging, to the surface. Oil-based mud consists of mineral oil, barite, bentonite and other additives such as emulsifying agents and polymers.
In the past, drill cuttings, especially if coming from off-shore platforms, were discharged into the sea creating an unacceptable environmental impact level. There are also great problems for dispersion on land. Various methods are used for removing oil mud from cuttings: among these are washing systems with detergents, thermal and distillation systems. The main disadvantages of these methods are respectively linked to poor efficiency, limited safety, mainly in offshore platforms, high costs and plant construction complexity.
It has now been found that the oil part of cuttings can be removed with a method which uses a simple solvent obtaining a mud which, with the optional addition of additives if necessary, can be re-used in other drillings whereas the soil can be returned to the environment.
In accordance with this, an objective of the present invention is a method for the removal of the oil component which contaminates drill cuttings and the recovery of oil-based drilling mud, comprising the following steps:
(a) mixing said cuttings with an organic solvent in a ratio ranging from 0.5 to 2, based on the weight of the cuttings thereby forming a mixture of a first solid phase, and a first liquid phase comprising the organic solvent and the oil;
(b) separating the first liquid phase from the first solid phase;
(c) separating the organic solvent from the oil in the separated first liquid phase of step (b);
(d) mixing the separated first solid phase of step (b) with the separated organic solvent of step (c), thereby forming a second solid phase, and a second liquid phase comprising the organic solvent and the oil;
(e) separating the second liquid phase from the second solid phase;
(f) separating the organic solvent from the oil in the separated second liquid phase of step (e);
(g) combining the separated oil of step (c) with the separated oil of step (f);
(h) evaporating residual solvent from the second solid phase;
(i) disposing of said evaporated second solid phase;
(j) preparing an oil-based drilling mud comprising the combined oil of step (g).